class MulLayer:
    def __init__(self):
        self.x = None
        self.y = None

    def forward(self,x,y):
        self.x = x 
        self.y = y
        out = x*y

        return out 
    
    def backward(self,dout):
        dx = dout * self.y 
        dy = dout * self.x 

        return dx,dy 
    
class AddLayer:
    def __init__(self):
        pass 
    def forward(self,x,y):
        return x+y 
    def backward(self,dout):
        dx = dout * 1
        dy = dout * 1
        return dx,dy 